o AV to AV interaction animations, both PG and M
o The ability to target another avatar and make it focus of your avatar's actions and emotes. This works very well in Star Wars Galaxies. When I dance in a cantina people come in and target me. Their avatars look at my avatar and slowly begin to clap to the rythm of the music I play. If in return I target them, my AV will look at them while performing, smile at them when I use a smile emote, blow them a kiss if I use that animated emote and so on.
o Targeted emotes: I want to type "/emote hug %TT" while targeting, say, an avatar named Gerald and have to following displayed:
"You hug Gerald" (on my screen)
"Anshe hugs you" (on Gerald's screen)
"Anshe hugs Gerald" (on other peoples screen)
For custom emotes I want to be able to type "/me teases %TT" and be able to read:
"Anshe teases Gerald" (on my screen)
"Anshe teases you" (on Gerald's screen)
"Anshe teases Gerald" (on everybody else's screen)
I used to make very very heavy use of this feature in SWG and the lack of it in SL seriously limits my roleplaying everytime more than one other person is listening.
o Sensitive scriptable spots on avatar surfaces. It would be very very nice if I could make my AV use her fingers, hands, feet, lips, teeth, tongue and at least one more fun part of her body to "touch", "tease", "bite", "scratch", "lick", "stroke", "hit", "suck", "beat" etc another AVs body parts and sensitive spots "tenderly", "lovingly", "brutaly" etc.

For example I would like to type: "/lefthand tease Gerald leftfoot playfully" and see how my AV's hand moves to Gerald's foot and a text message is displayed such as "You playfully tease Gerald's left foot" while Gerald could read "Anshe playfully teases your left foot".
In addition, AV's could have emotional reactions scripted to specific manipulations of their sensory spots. For example when Anshe runs her fingers through Gerald's hair lovingly (/fingers runthrough Gerald hair lovingly) you would not only see my AV's hand touch Gerald's hair and the message "Anshe runs her fingers through your hair lovingly" on Gerald's screen, but he may also get a message like "You feel warm and comfortable"

o Emotional state of an avatar would be nice
Which would be possible to manipulate/set through the player (such as in SWG) and maybe even through events (such as touches on sensitive spots, music, noise, injury,...) 
o Consensual transfer of control. It would be nice to have the ability for AVs to temporarily restrain or force other AVs. This would be fun for PvP games and also some very popular M roleplaying activities. It just adds to the thrill and sense of realism to enter a vampire castle, get trapped unable to move and then biten by a nasty vampire AV there, while unable to run away and screaming with fear
Of course no effects should be permanent and nobody should be forced to enter such (clearly marked) vampire castles
You have some of this in PvP games such as snare, stun, blindness, poison, drunkness and so on 